Diffusion media, fuel cells, and fuel cell powered systems

ABSTRACT

In at least certain embodiments, the present invention provides a diffusion media and fuel cells and systems employing the diffusion media. In at least one embodiment, the diffusion media comprises a porous matrix having an outer surface and a hydrophilic polymeric coating on at least a portion of the porous matrix with the hydrophilic coating comprising the cured product of a formulation comprising a hydrophilic monomer.

FIELD Of THE INVENTION

The present invention relates generally to diffusion media, fuel cellsemploying diffusion media according to the present invention, and fuelcell powered systems utilizing such fuel cells. More specifically, thepresent invention is related to the use of diffusion media in addressingwater transport difficulties in fuel cells and other types of devices.

Background Art

Fuel cells have been used as a power source in many applications andhave been proposed for use in electrical vehicular power plants toreplace internal combustion engines. In proton exchange membrane (PEM)type fuel cells, hydrogen is supplied to the anode of the fuel cell andoxygen is supplied as the oxidant to the cathode. PEM fuel cells includea membrane electrode assembly (MEA) comprising a thin, protonconductive, non-electrically conductive solid polymer electrolytemembrane having the anode on one of its faces and the cathode on theopposite face. The MEA is sandwiched between a pair of electricallyconductive elements which (1) serve as current collectors for the anodeand cathode, and (2) contain appropriate channels and/or openingstherein for distributing the fuel cell's gaseous reactants over thesurfaces of the respective anode and cathode catalysts. A plurality ofindividual cells are commonly bundled together to form a PEM fuel cellstack. The term fuel cell is typically used to refer to either a singlecell or a plurality of cells (stack) depending on the context. A groupof cells within the stack is typically referred to as a cluster. Typicalarrangements of multiple cells in a stack are described in U.S. Pat. No.5,763,113, assigned to General Motors Corporation.

In PEM fuel cells hydrogen (H₂) is the anode reactant (i.e., fuel) andoxygen is the cathode reactant (i.e., oxidant). The oxygen can be eithera pure form (O₂), or air (a mixture of O₂ and N₂). The solid polymerelectrolytes are typically made from ion exchange resins such asperfluorinated sulfonic acid ionomers. The anode/cathode typicallycomprises finely divided catalytic particles, which are often supportedon carbon particles, and admixed with a proton conductive resin. Thecatalytic particles are typically costly precious metal particles. Thesemembrane electrode assemblies, which comprise the catalyzed electrodes,require certain controlled conditions in order to maintain certainhydration for optimized proton conductivity and avoid flooding.

Efficient operation of a fuel cell depends, at least in part, on theability to effectively disperse reactant gases at catalytic sites of theelectrode where reaction occurs. In addition, effective removal ofproduct water is desired so as to not inhibit flow of fresh reactants tothe catalytic sites. Therefore, it is desirable to improve the mobilityof reactant and product water to and from the MEA where reaction occurs.

To improve the mobility of reactant and product species to and from theMEA where reactions occur, a diffusion structure which enhances masstransport to and from an electrode in a MEA of a fuel cell is used. Thediffusion structure cooperates and interacts with an electrode at amajor surface of the electrode opposite the membrane electrolyte of thecell, therefore, electrical and heat conductivity are required. Thediffusion structure facilitates the supply of reactant gas to theelectrode. The diffusion structure is hereinafter referred to as adiffusion media. See for example U.S. Pat. No. 6,350,539 issued to theassignee of the present application. The diffusion media is positionedbetween the MEA and the cathode or anode flow channels of an individualfuel cell. One example of a relatively typical diffusion media comprisesan electrically conductive porous media such as carbon paper.

In an operating PEM fuel cell, water is generated at the cathode sidedue to the electrochemical reaction between hydrogen and oxygenoccurring within the MEA. Water is also typically introduced throughreactant gas streams into fuel cells to humidify the membrane to ensuregood proton conductivity. PEM fuel cells can experience a relativeexcess of water, which, if not removed from the system, could block thetransportation path between oxidant gas and cathode electrode. Inaddition to possible oxidant starvation on the cathode side, water slugsin the gas flow channel may also be formed on the anode side which cancause hydrogen starvation. Water on the anode side can result fromexternal humidification of the hydrogen gas and from back diffusionthrough the membrane (cathode to anode). If these occur, the fuel cellefficiency can decrease and may eventually lead to system shutdown, aphenomenon called “flooding.” Managing water is therefore a relativelyimportant aspect for the efficient operation of a fuel cell.

The diffusion media plays a relatively important role in PEM fuel cellswater management. The diffusion media can facilitate movement of waterto ensure good transportation paths between reactant gases and catalystelectrodes in the MEA. One conventional practice to accomplish this isto coat the diffusion media (such as carbon paper) with a hydrophobicmaterial such as polytetrafluoroethylene (PTEE). This PTEE coating makesthe media more hydrophobic and thus helps to prevent water from blockingthe flow channels in diffusion media. Even still, other water managementproperties are sought to provide more efficient water management. Itwould be desirable for the gas diffusion media to provide a flow pathfor increased water management in a fuel cell.

SUMMARY OF THE INVENTION

In at least one embodiment, the present invention comprises a porousmatrix having an outer surface comprising a first major face and asecond major face and a hydrophilic polymeric coating on at least aportion of the porous matrix wherein the hydrophilic coating comprisesthe cured product of a formulation comprising a hydrophilic monomer.

In at least another embodiment, the present invention comprises a fuelcell comprising an anode, a cathode, a PEM disposed between the anodeand the cathode, and a diffusion media disposed between at least one ofthe anode and the cathode and the PEM. The diffusion media comprises aporous matrix having an outer surface comprising a first major face anda second major face and a hydrophilic polymeric coating on at least aportion of the outer surface. The hydrophilic coating comprises thecured product of a formulation comprising a hydrophilic monomer.

In at least yet another embodiment, the present invention comprises amethod for making a diffusion media. The method comprises providing aporous matrix and coating at least a portion of the porous matrix with ahydrophilic polymeric coating. In at least one embodiment, the coatingstep comprises exposing the porous matrix to a hydrophilic formulationcomprising a hydrophilic monomer to form a coating precursor on theporous matrix, masking a first portion of the precursor coated porousmatrix while leaving a second portion of the matrix unmasked, andexposing the precursor coated porous matrix to UV light to UV cure thecoating precursor on the second portion of the matrix to form thehydrophilic polymeric coating on the second portion.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided herein. It should beunderstood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings where like structureis indicated with like reference numerals and in which:

FIG. 1 is an exploded schematic illustration of a fuel cellincorporating a porous diffusion media according to the presentinvention;

FIG. 2 is an illustration of a diffusion media according to embodimentsof the present invention;

FIG. 3 is an illustration of a diffusion media according to embodimentsof the present invention positioned against a catalyst layer;

FIG. 4 is a schematic representation of a diffusion media according toother embodiments of the present invention; and

FIG. 5 is an illustration of a vehicle incorporating a fuel cellemploying a porous diffusion media according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. Reference will now be made in detail topresently preferred compositions, embodiments and methods of the presentinvention, which constitute the best modes of practicing the inventionpresently known to the inventors. The figures are not necessarily toscale. However, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. Therefore, specific details disclosed herein arenot to be interpreted as limiting, but merely as a representative basesfor the claims and/or as a representative basis for teaching one skilledin the art to variously employ the present invention.

Except in the examples, or where otherwise expressly indicated, allnumerical quantities in this description indicating amounts of materialor conditions of reaction and/or use are to be understood as modified bythe word “about” in describing the broadest scope of the invention.Practice within the numerical limits stated is generally preferred.Also, unless expressly stated to the contrary: percent, “parts of”, andratio values are by weight; the term “polymer” includes “oligomer”,“copolymer”, “terpolymer”, and the like; the description of a group orclass of materials as suitable or preferred for a given purpose inconnection with the invention implies that mixtures of any two or moreof the members of the group or class are equally suitable or preferred;description of constituents in chemical terms refers to the constituentsat the time of addition to any combination specified in the description,and does not necessarily preclude chemical interactions among theconstituents of a mixture once mixed; the first definition of an acronymor other abbreviation applies to all subsequent uses herein of the sameabbreviation and to normal grammatical variations of the initiallydefined abbreviation; and, unless expressly stated to the contrary,measurement of a property is determined by the same technique aspreviously or later referenced for the same property.

Referring initially to FIG. 1, an exemplary fuel cell 10 incorporatingporous diffusion media 20 according to the present invention isillustrated. Specifically, the fuel cell 10 comprises a membraneelectrode assembly 30 interposed between an anode flow field 40 and acathode flow field 50 of the fuel cell 10. It is contemplated that theflow fields 40, 50 and the membrane electrode assembly 30 may take avariety of conventional or yet to be developed forms without departingfrom the scope of the present invention. Although the particular form ofthe membrane electrode assembly 30 is beyond the scope of the presentinvention, in the illustrated embodiment, the membrane electrodeassembly 30 includes respective catalytic electrode layers 32 and an ionexchange membrane 34.

Referring to FIG. 2, a porous diffusion media 20 according to oneembodiment of the present invention is illustrated. The diffusion media20 comprises a porous matrix 22 having a hydrophilic polymeric coating24 on at least a portion of the surface of the porous matrix. In atleast one embodiment, the hydrophilic polymeric coating 24 comprises acured polymer suitable to result in a contact angle for the coated media20 of less than 90°, in other embodiments of less than 75°, in yet otherembodiments of less than 50°, in still yet other embodiments of lessthan 25°, in still yet other embodiments of less than 15°, in still yetother embodiments of less than 10°, in still yet other embodiments ofless than 5°, and in still yet other embodiments of 0°. The hydrophiliccoating 24 can provide an efficient water flow path through the media 20to wick water away. A contact angle of 0° for a porous media means thatwater will essentially immediately travel or wick through the diffusionmedia 20.

In at least one embodiment, the coating 24 is a hydrophilic,polymerized, cross-linked monomer that renders the coated matrix 22hydrophilic, (i.e., having a contact angle less than 90°). The monomercan be deposited on the surfaces of the porous matrix 22 by graftpolymerization and/or by deposition of the cross-linked monomer. In atleast one embodiment, the coating 24 can be between 1 nm (nanometer) and1 μm (micron) thick, in another embodiment between 5 and 100 nm thick,and in still yet another embodiment between 10 and 50 nm thick. Atthicknesses below 1 nm, the matrix 22 may not be sufficientlyhydrophilic. At thicknesses above 1 micron, the permeability of thematrix 22 can be impaired.

The porous matrix 22 may comprise any suitable porous matrix material,such as an electrically conductive material, carbon paper, graphitepaper, cloth, felt, foam, carbon or graphite wovens, carbon or graphitenon-wovens, metallic screens or foams, and combinations thereof.Although the dimensions of the matrix 22 will depend largely upon thedesign requirements associated with the particular application in whichthe porous diffusion media 20 is to be utilized it is noted thatthicknesses d of between 20 μm and 1000 μm or, more particularly, 200μm, are likely to find utility. Similarly, by way of illustration andnot limitation, the porous matrix may define a porosity characterized bya permeometer number (as measured with a Gurley Permeometer, model no.4301) of 50 ft³/min./ft² at 0.5 inches of water or, more generally, aGurley permeometer number of between 20 ft.³/min./ft.² and 100ft.³/min./ft.² at 0.5 inches of water. In this context, it is noted thatporosity is the measure of how easily air can pass through a sample ofmaterial. The Gurley test measures the time needed to pass a givenvolume of air through the sample.

The polymerization and cross-linking of the polymerizable monomer to theporous matrix 22 by grafting and/or deposition may be effected so thatsubstantially the entire surface of the porous matrix including theinner surfaces of the pores (i.e., across the porous matrix thickness dor bulk) is coated entirely with a cross-linked/grafted polymer.Alternatively, the coating 24 may be limited to less than the entiresurface of the matrix 22, such as a portion of the entire surface orbulk (less than d, such as one-half of d), one or both sides of thematrix 22, portions of one or both sides of the matrix 22, and/or stripsor other discrete shapes of coverage.

In one process embodiment, a reagent bath comprising a free radicalpolymerizable monomer, a polymerization initiator and cross-linkingagent in a solvent or other suitable diluent for the reactantconstituents is contacted with the porous matrix 22. The treated matrix22 is then placed under conditions to effect free radical polymerizationof the monomer and coating of the porous matrix with the cross-linkedpolymer. When the monomer is difunctional or has higher functionality,an additional cross-linking agent need not be utilized.

Any monomer for coating the polymer can be utilized herein so long as itis hydrophilic, capable of being polymerized by free radicalpolymerization, and can be cross-linked. Suitable hydrophilic monomersinclude, but are not limited to, hydroxyl substituted ester acrylate andester methacrylate, including but not limited to 2-hydroxyethylacrylate,2- and 3-hydroxypropylacrylate, 2,3-dihydroxypropylacrylate,polyethoxyethyl-, and polyethoxypropylacrylates; acrylamide,methacrylamide and its derivatives, including but not limited toN-methylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide,N,N-dimethyl-aminoethyl, N,N-diethyl-aminoethyl,2-acrylamido-2-methyl-1-propanesulfonic acid,N-[3-dimethylamino)propyl]acrylamide, and 2-(N,N-diethylamino)ethylmethacrylamide; polyethylene glycol acrylates, polyethylene glycolmethacrylates, polyethylene glycol diacrylates, polyethylene glycoldimethacrylates; polypropylene glycol acrylates, polypropylene glycolmethacrylates, polypropylene glycol diacrylates, polypropylene glycoldimethacrylates; acrylic acid; methacrylic acid; 2- and 4-vinylpyridine;4- and 2-methyl-5-vinylpyridine; N-methyl-4-vinylpiperidine;2-methyl-1-vinylimidazole; dimethylaminoethyl vinyl ether;N-vinylpyrrolidone; itaconic, crotonic, fumaric and maleic acids;styrene sulfonic acid and mixtures thereof. In at least one embodiment,a particularly suitable monomer comprises polyethylene glycol acrylate.

Suitable cross-linking agents for the monomers set forth above are wellknown in the art. Suitable agents include, but are not limited to,monomers having di- or multi-unsaturated functional groups, includingbut not limited to diacrylates and dimethylacrylates of -polyethyleneglycol and -polypropylene glycol, trimethylolpropane triacrylate andtrimethacrylate, di-trimethylolpropane, tetraacrylate, pentaerythritoltetraacrylate, tetramethacrylate, divinylbenzene, divinyl sulfonesilicone-containing diacrylates and dimethacrylates. In at least oneembodiment, a particularly suitable cross-linking agent comprisespolyethylene glycol diacrylate.

Suitable initiators for the monomers set forth above are well known inthe art. Suitable initiators include, but are not limited to, ammoniumpersulfate, potassium persulfate, 4,4′-azobis(4-cyanovaleric acid),2,2′-azobis(2-amidinopropane) hydrochloride, potassium hydrogenpersulfate, ketones or the like. In at least one embodiment, aparticularly suitable cross-linking agent comprises ketone, such as CibaSpecialty Chemicals IRGACURE 184 (1-hydroxy-cycle-phenyl-ketone).

The particular solvent composition or diluent employed for thepolymerizable monomer, polymerization initiator and cross-linking agentwill depend upon the particular reactants employed. All that isnecessary is that the reactants dissolve in the solvent and that thesolvent does not attack the porous matrix 22. Representative suitablesolvent compositions include (a) water and (b) a water-miscible organicsolvent such as N-methylpyrrolidone, dimethyl sulfoxide, isopropanol,2-propanol, tetrahydrofuran, propylene carbonate, gammabutyrolactone,tetrahydrothiophene-1,1-dioxide, N-cyclohexyl-2-pyrrolidone,tetramethylurea or the like.

Generally, the polymerizable monomer can generally be present in thereactant solution in at least one embodiment at a concentration ofbetween 1% and 100% by weight, in another embodiment between 5% and 50%by weight, and in yet another embodiment between 10% and 30% by weight,based upon the weight of the reactant solution. In at least oneembodiment, the cross-linking agent can generally be present in anamount of between 0.5% and 100% by weight, in another embodiment between1% and 25% by weight, and in yet another embodiment between 2% and 10%by weight, based upon the weight of the reactant solution. In at leastone embodiment, the polymerization initiator can generally be present inan amount of between 0.01% and 10% by weight, in another embodimentbetween 0.5% and 5% by weight, and in yet another embodiment between 1%and 3% by weight, based upon the weight of the reactant solution. Asnoted above, the cross-linking agent can be utilized without the monomerand thereby could function as the polymerizable monomer.

Any conventional energy source for initiating free radicalpolymerization can be employed such as ultraviolet light, heating, gammaradiation, electron beam radiation or the like. In at least oneembodiment, the polymerization reaction should be effected for a time toassure that the desired surface of the porous matrix 22 is coated withthe deposited polymer composition but without substantially plugging thepores in the. matrix 22. In at least one embodiment, the hydrophilicpolymeric coating 24 reduces the gas permeability of the porous matrix22, relative to its initial gas permeability, by less than 40%, in otherembodiments by less than 25%, and in yet other embodiments by less than15%. Generally, in at least one embodiment, suitable reaction times arebetween 0.1 and 30 minutes, and in other embodiments, between 1 and 4minutes. Reaction could be effected while the porous matrix 22 isimmersed in solution. However, this could likely result in thepolymerization of the monomer throughout the solution. It is preferredto saturate the porous matrix 22 with the reactant solution and toeffect reaction outside of the solution so that monomer is not wasted.Thus, the reaction can be conducted batchwise or continuously. Whenoperating as a continuous process, a sheet of porous matrix 22 issaturated with the reactant solution and then transferred to a reactionzone where it is exposed to energy to effect the polymerizationreaction.

As set forth above, in at least one embodiment, the hydrophilicpolymeric coating 24 may be disposed on the entire surface of the porousmatrix 22. In at least another embodiment, the hydrophilic polymericcoating 24 may be disposed on less than the entire surface of the porousmatrix 22. For instance, in at least certain embodiments, thehydrophilic polymeric coating 24 may be disposed on one or both of themajor face 21 or 23 of the matrix 22, or on a portion of one or both ofthe major faces 21, 23 of the matrix. Furthermore, in at least anotherembodiment, the hydrophilic polymeric coating 24 may be disposed onsubstantially all or portions of one or both major faces 21, 23 of thematrix 22 and extend substantially into the bulk of the matrix 22between the coated portions of the major faces 21, 23.

Referring collectively to FIGS. 2 and 4, certain embodiments areillustrated where exemplary spaced regions 26 of the hydrophilic coating24 can be distributed across a cross section of the porous diffusionmedia 20 between the first and second major faces 21, 23 of thediffusion media and may alternate across the first and second majorfaces 21, 23. In this embodiment, substantially uncoated regions 28 ofthe porous matrix 22 may be between the hydrophilic coated regions. Forillustrative purposes, and not by way of limitation, it is noted thataccording to one embodiment of the present invention the spacedhydrophilic coating regions 26 can be characterized by a periodicity ofless than 5.0 cm, according to another embodiment of less than 1.0 cm,according to yet another embodiment of 0.5 cm, and according to stillyet another embodiment of 0.25 cm. Of course, the periodicity, shapes,and relative sizes of the hydrophilic regions 26 depend largely upon thedesign requirements associated with the particular application in whichthe porous diffusion media 20 is to be utilized.

The spaced configuration of the hydrophilic coating regions 26 of thepresent invention, as exemplarily illustrated in FIGS. 2-4, can limitthe interference between water and gas transfer by providing fordivision of the diffusion media 20 into regions 26 where water transferis emphasized and regions 28 where gas transfer is emphasized.

In certain embodiments of the present invention, the hydrophilic regions26 may be defined as being sufficiently hydrophilic to define contactangle of less than 90°, in other embodiments of less than 75°, in yetother embodiments of less than 50°, in still yet other embodiments ofless than 25°, in still yet other embodiments of less than 15°, in stillyet other embodiments of less than 10°, in still yet other embodimentsof less than 5°, and in still yet other embodiments of 0°.

As is also illustrated in FIGS. 2-4, in at least certain embodiments,the porous diffusion media 20 may comprise hydrophobic material 25, suchas in the form of a hydrophobic layer, disposed along at least a portionof one of, such as the second major face 23, the diffusion media 20. Thehydrophobic material 25 typically forms a relatively thin hydrophobiccoating layer on the surfaces of the porous matrix 22, e.g., up to 1 μmin thickness, without significantly reducing gas permeability of theporous matrix 22. In the illustrated embodiment, the hydrophobicmaterial 25 can help to prevent accumulation of liquid water droplets onthe diffusion media 20. It is contemplated that it may be preferable toensure that the hydrophobic material 25 be more repellent to waterdroplets, i.e., more hydrophobic, than both the coated and uncoatedregions 26, 28 of the porous diffusion media 20.

The hydrophobic material 25 is normally comprised of a fluoropolymer. Byway of illustration and not limitation, suitable fluoropolymers may beproduced from tetrafluoroethylene (TFE), hexafluoropropylene (HFP),ethylene and tetrafluoroethylene (ETFE), fluorinated ethylene andpropylene (FEP), a perfluoromethyl vinyl ether, vinylidene fluoride, andthe like, and combinations thereof.

In at least one embodiment, the hydrophilic polymeric coating 24 and thehydrophobic material 25 may be disposed in discrete patterns about theporous matrix 22 to create regions in the diffusion media 20 where watertransfer is emphasized and where gas transfer is emphasized. In thistype of configuration, water transfer would be emphasized at theportions 26 of the matrix 22 coated with the hydrophilic coatings 24 andthe gas transfer would be emphasized at the areas 28 coated with thehydrophobic material 25.

In at least one embodiment, the diffusion media 20 of the presentinvention is made by exposing the porous matrix 22 to a solution ofsolvent (if necessary), hydrophilic monomer, crosslinker (if necessary)and preferably an initiator. In at least one embodiment, the porousmatrix 22 is exposed to the solution by dipping the porous matrix 22 inthe solution. The treated porous matrix 22 can then be allowed to dry tolet any solvent evaporate to leave the treated porous matrix 22 with acoating precursor thereon. The porous matrix 22 with the coatingprecursor thereon can then be exposed to a curing medium, such as Lwlight, to cure coating 24 onto the porous matrix 22 to form thediffusion media 20.

In an alternative embodiment, selective placement of the hydrophiliccoating 24 can be accomplished by covering the porous matrix 22 with thecoating precursor thereon with a suitable mask, such as a metal orplastic plate, and then exposing the mask porous matrix 22 to a suitablecuring medium to cure the uncovered (i.e., unmasked) portions of theporous matrix 22. In this embodiment, a particularly suitable curingmedium is UV light since the UV light will not cure the coatingprecursor covered by the mask. After removing the mask, the porousmatrix 22 with the predetermined coating layers 24 can then be exposedto a rinsing with solvent to remove the uncured coating precursor fromthe porous matrix 22. The porous matrix 22 with the portions that arecoated with a hydrophilic coating 24 can then be allowed to dry to formthe diffusion media. Also, it is contemplated that an alternative tousing a mask can be to selectively apply the hydrophilic monomersolution only to discrete areas 26 to be coated with the hydrophiliccoating 24. If desired, the hydrophobic material 25 can be disposed onor secured to the diffusion media 20 in any suitable manner, eitherbefore or after being coated with the hydrophilic coating 24. Ifhydrophobic material 25 is employed, it can be disposed on the media 20in any suitable manner, such as by vapor phase PTFE deposition.

Referring to FIG. 5, it is noted that devices according to the presentinvention may include additional structure defining a fuel cell poweredmotor vehicle 100, in combination with a fuel cell 10 according to thepresent invention and a fuel storage mechanism 15. It is to beappreciated, however, that other fuel cell system applications, such asfor example, in the area of residential systems, may benefit from thepresent invention.

The present invention will be further explained by way of example. It isto be appreciated that the present invention is not limited by theexample.

EXAMPLE

A formulation of hydrophilic coating composition is prepared comprising0.1 grams of polyethylene glycol diacrylate (PEGDA), 0.4 grams ofpolyethylene glycol acrylate (PEGA), 0.02 grams of the photoinitiatorIrgacure 184 (available from Ciba Specialty Chemicals) and 1.5milliliters of isopropanol. A carbon fiber diffusion media is thenimmersed in the solution for one minute. The diffusion media is thenremoved from the solution and exposed to air for five minutes toevaporate the isopropanol solvent. The treated diffusion media is thenexposed to UV curing.

In order to test durability of the hydrophilic coating, the diffusionmedia with the hydrophilic coating is exposed to water heated to 95° C.for three days and then thereafter exposed to an acidic solution ofwater (pH=2) at 95° C. for three days. After exposure to water and theacidic solution of water, the diffusion media remains hydrophilicindicating that the hydrophilic coating is very stable and suitablyadhered to the porous matrix of the diffusion media.

It is noted that terms like “preferably,” “commonly,” and “typically”are not utilized herein to limit the scope of the claimed invention orto imply that certain features are critical, essential, or evenimportant to the structure or function of the claimed invention. Rather,these terms are merely intended to highlight alternative or additionalfeatures that may or may not be utilized in a particular embodiment ofthe present invention.

For the purposes of describing and defining the present invention it isnoted that the term “substantially” is utilized herein to represent theinherent degree of uncertainty that may be attributed to anyquantitative comparison, value, measurement, or other representation.The term “substantially” is also utilized herein to represent the degreeby which a quantitative representation may vary from a stated referencewithout resulting in a change in the basic function of the subjectmatter at issue.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention. Furthermore, although some aspects ofthe present invention are identified herein as preferred or particularlyadvantageous, it is contemplated that the present invention is notnecessarily limited to these preferred aspects of the invention.

1. A porous diffusion media comprising: a porous matrix having an outersurface comprising a first major face and a second major face; and, ahydrophilic polymeric coating on at least a portion of the outersurface; the hydrophilic coating comprising the cured product of aformulation comprising a hydrophilic monomer.
 2. The porous diffusionmedia of claim 1 wherein the hydrophilic coating is sufficientlyhydrophilic to define a contact angle of less than 90° along one of thefirst and second major faces of the diffusion media.
 3. The porousdiffusion media of claim 1 wherein the hydrophilic coating issufficiently hydrophilic to define a contact angle of less than 25°along one of the first and second major faces of the diffusion media. 4.The porous diffusion media of claim 1 wherein the hydrophilic coating issufficiently hydrophilic to define a contact angle of 0° along one ofthe first and second major faces of the diffusion media.
 5. The porousdiffusion media of claim 1 wherein the porous matrix comprises anelectrically conductive material comprising at least one of: carbonpaper, graphite paper, cloth, felt, foam, carbon or graphite wovens,carbon or graphite non-wovens, metallic screens or foams, andcombinations thereof.
 6. The porous diffusion media of claim 4 whereinthe porous matrix defines a thickness of between 20 μm and 1000 μm andthe hydrophilic coating has a thickness between 1 nm and 1 μm.
 7. Theporous diffusion media of claim 2 wherein the outer surface includes aninner surface portion extending between the first and second majorfaces, the coating being disposed on the inner surface portion andextending between the first and second major faces.
 8. The porousdiffusion media of claim 7 wherein the hydrophilic monomer comprises aglycol acrylate or glycol methacrylate.
 9. The porous diffusion media ofclaim 8 wherein the hydrophilic monomer comprises polyethylene glycolacrylate.
 10. The porous diffusion media of claim 7 wherein thehydrophilic monomer is UV curable.
 11. The porous diffusion media ofclaim 10 wherein the formulation comprises polyethylene glycol acrylate,polyethylene glycol diacrylate, photoinitiator, and solvent.
 12. Theporous diffusion media of claim 1 wherein the porous diffusion mediafurther comprises hydrophobic material.
 13. The porous diffusion mediaof claim 12 wherein the hydrophobic material is disposed along one ofthe first and second major faces of the diffusion media.
 14. The porousdiffusion media of claim 1 wherein the hydrophilic coating has portionsdistributed across a cross section of the porous diffusion media betweenfirst and second major faces of the diffusion media.
 15. The porousdiffusion media of claim 1 wherein the hydrophilic polymeric coatingcomprises regions of hydrophilic polymeric coating and the diffusionmedia comprises uncoated regions, the regions of the hydrophilicpolymeric coating and the uncoated regions alternate across at least oneof first and second major faces of the diffusion media.
 16. The porousdiffusion media of claim 12 wherein the hydrophilic polymeric coatingcomprises regions of hydrophilic polymeric coating and the hydrophobicmaterial comprises regions of hydrophobic material.
 17. The porousdiffusion media of claim 16 wherein the alternating regions arecharacterized by a periodicity of less than 5 cm.
 18. A fuel cellcomprising: an anode; a cathode, a PEM disposed between the anode andthe cathode; and a diffusion media disposed between at least one of theanode and the cathode and the PEM, the diffusion media comprising: aporous matrix having an outer surface comprising a first major face anda second major face; and a hydrophilic polymeric coating on at least aportion of the outer surface; the hydrophilic coating comprising thecured product of a formulation comprising a hydrophilic monomer.
 19. Amethod for making a diffusion media, said method comprising: providing aporous matrix; and coating at least a portion of the porous matrix witha hydrophilic polymeric coating.
 20. The method of claim 19 wherein thecoating step comprises: exposing the porous matrix to a hydrophilicformulation comprising a hydrophilic monomer to form a coating precursoron the porous matrix; masking a first portion of the precursor coatedporous matrix while leaving a second portion of the matrix unmasked; andexposing the precursor coated porous matrix to UV light to UV cure thecoating precursor on the second portion of the matrix to form thehydrophilic polymeric coating on the second portion.